1. Field of the Invention
This invention relates to a reproducing apparatus adapted for reproducing information signals from a record bearing medium having a plurality of recording tracks in which the information signals are recorded.
2. Description of the Prior Art
Information signal reproducing apparatuses include a kind arranged to bring a reproducing head onto a recording track by using a pilot signal reproduced by the reproducing head from a record bearing medium on which a plurality of pilot signals of different frequencies are cyclically recorded in the recording tracks together with information signals. For the reproducing apparatus of this kind, there have been known various methods for setting the plurality of pilot signals. An example of such methods is called a four frequency method. This method is as described below with reference to the accompanying drawings:
FIG. 1 shows reproducing heads of a conventional video tape recorder (VTR for short) in a state of tracing the recording tracks of a record bearing medium T on which a video signal is recorded together with pilot signals of four different frequencies f1, f2, f3 and f4. The illustration includes also cross-talk signals coming from adjacent tracks on the left and right sides of each mainly traced track. FIG. 2 is a block diagram showing the essential arrangement of the tracking control circuit of the same VTR. The frequencies f1, f2, f3 and f4 are arranged such that a frequency difference between any two of the four different pilot signals is either .DELTA.fa or .DELTA.fb. In other words, a reference signal which is generated by a reference signal oscillator 127 (OSC for short) is frequency divided, by frequency dividers 101, 102, 103 and 104, each having a different frequency dividing ratio. A switch 109 has four terminals which are arranged to receive signals of frequencies f1, f2, f3 and f4 obtained by allowing the frequency divided reference signals to pass through band-pass filters 105, 106, 107 and 108 having the frequencies f1, f2, f3 and f4 at the centers of their pass bands, respectively. These frequencies are set within a frequency band lower than that of the video signal. The switching operation of the switch 109 is arranged to be performed in a cyclic manner at every rise and fall of a rectangular wave signal (hereinafter referred to as the 30 PG signal) which is in synchronism with the rotating period of rotary heads 100a and 100b. More specifically, the use of the rotary heads 100a and 100b is changed over by a head switching circuit 123 in synchronism with the 30 PG signal in such a manner as 100a.fwdarw.100b.fwdarw.100a.fwdarw.100b.fwdarw.100a . . . . Then, also in synchronism with the 30 PG signal, the switch 109 shifts its output in such a manner as the signals of frequencies f1.fwdarw.f2.fwdarw.f3.fwdarw.f4.fwdarw.f1.fwdarw.. . . . The above-stated 30 PG signal is produced from a 30 PG signal oscillator 125 in synchronism with the rotating period of the heads 100a and 100b, which is detected by a detector 124.
During a recording operation, the signals of frequencies f1, f2, f3 and f4 are frequency mixed at a mixing circuit 129 with the video signal which has been processed by a signal processing circuit 130 for recording. The frequency mixed signal thus obtained is amplified by a recording amplifier 131 before being supplied to the rotary heads 100a and 100b through a recording/reproduction change-over switch 128.
At the time of reproduction, the signals of frequencies f1, f2, f3 and f4 are reproduced by the rotary heads through the head switching circuit 123 in synchronism with the 30 PG signal from a magnetic tape 126 which is used as the record bearing medium and has the video signal together with the signals of frequencies f1, f2, f3 and f4 thereon. A reproduction signal thus obtained is supplied to an amplifier 110 through the recording/reproduction change-over switch 128. Then, a frequency component including the band of the video signal is separated by a high-pass filter (HPF) 132 and is supplied to a signal processing circuit 133. The circuit 133 then performs a reproduction signal processing operation on this frequency component and produces it as a reproduced video signal. Meanwhile, another frequency component including the frequencies f1, f2, f3 and f4 is separated through a low-pass filter (LPF) 111 and is supplied to a multiplier 112. The multiplier 112 multiplies the output signal of the LPF 111 by reference signals of frequencies f1, f2, f3 and f4 which are cyclically supplied via a switch 109. The multiplier 112 thus produces signals including the frequency difference components .DELTA.fa and .DELTA.fb. The frequency components included in the signals .DELTA.fa and .DELTA.fb are obtained from the following relation (wherein f1&lt;f2&lt;f4&lt;f3): EQU .vertline.f1-f2.vertline.=.DELTA.fa EQU .vertline.f2-f3.vertline.=.DELTA.fb EQU .vertline.f3-f4.vertline.=.DELTA.fa EQU .vertline.f4-f1.vertline.=.DELTA.fb
To extract the difference frequencies .DELTA.fa and .DELTA.fb, the tracking control circuit is provided with band-pass filters 113 and 114 and detectors 115 and 116, for these difference frequencies .DELTA.fa and .DELTA.fb. Then an output level difference between the two difference frequencies becomes zero, the reproducing head 100 is considered to be accurately tracing the recording track, that is, the head is considered to be in an on-track state. For this purpose, the output level difference between the difference frequencies .DELTA.fa and .DELTA.fb are detected by means of a differential amplifier 117 and, as a result of this, a tracking error signal voltage E.sub.0 is obtained.
Again referring to FIG. 1, hatched parts indicate that the positions of the difference frequencies .DELTA.fa and .DELTA.fb relative to the reproducing head are interchanging every time the positions of the heads shift from one track to another. Therefore, in order to detect the deviating (or error) direction of the rotary heads 100a and 100b, the positive and negative polarities of the phase of the above-stated error signal voltage E.sub.0 must be inverted in synchronism with the above-stated rectangular wave signal (or 30 PG signal) which is synchronized with the rotation of the heads. The inverting operation is performed by the combination of an inverter 118 and an electronic switch 119 which are shown in FIG. 2 to obtain an error signal voltage E.sub.1. The error signal voltage E.sub.1 includes the direction of the error and the extent of the deviation. Further, a control voltage E.sub.2 which is required for driving a capstan motor 122 at a constant speed is added to the error voltage E.sub.1 by an adder 121 to obtain a tracking control signal voltage E.sub.3. This control signal voltage E.sub.3 is used to control the motor 122.
However, since the conventional apparatus described in the foregoing is arranged to perform error detection by obtaining the control signal voltage from two different frequencies, the circuit arrangement of the apparatus becomes complex.